Hi Torsten,
As a general rule of thumb a daily budget between 12$ and 15$ should cover basic costs (food, accommodation, transport). This excludes the many wonderful attractions such as visiting Machu Picchu.
Quito has many great Spanish schools. You can check out this
Quito Spanish Language School package to get an idea. I myself followed a one-on one course in Quito for 2.50$/hour (no family home stay) but that's a long time ago.
Hiking the Inca Trail to Machu Picchu costs a few hundred dollars. Check out a
4-Day Inca Trail package. Only 500 permits are issued daily so it's best to book this in advance.
Climbing Cotopaxi was an awesome experience. Breathtaking. I got lucky when I shared a room in Quito with Jorge, an experienced mountain climber from Switzerland. He guided me to the top of Cotopaxi. Here is a
7-Day Cotopaxi Volcano Climb package.
Do google and check out local travel agents before setting with a package. Maybe someone else can share some travel agents with excellent packages.
Enjoy your trip! Keep us posted!
Best wishes,
Mark